170 GEOLOGY AND PETROGRAPHY OP CLAEENCETOWN-PATKESON DISTRICT, i., 



ing this is the most important unit in the sequence. It appears in the majority 

 of cases to be a dellenite, but in some places is a toscanite. It has a maximum 

 thickness of 400 feet, and occurs as a thick capping to most parts of the Mt. 

 Gilmore ridge. The variations in the lithological features seen in hand-specimen 

 would lead one to expect gTeater differences than are apparent under the micro- 

 scope. The distribution and chemical variation of this rock are indicated in the 

 account of the Regional Geology. 



Above the dellenite there are tuffs containing a thin band of red felsite 

 which may be intrusive. These are succeeded by a very characteristic cream or 

 white lava, which shows an abundance of stumpy felspar phenocrysts, and pecu- 

 liar spherulitic and axiolitio inclusions set in a dense base, examination in thin 

 section proving the rock to be a daeite. After an interval of 45 feet of red 

 tuffaceous conglomerate, a similar white rock occurs, probably also a daeite. 

 Above it there is a mass of conglomerate which is quite persistent along the ridge. 

 It contains well-rounded pebbles of quartzite, felspar-porphyry and aplite in 

 abundance, and is followed by a very distinctive lava, which here and elsewhere 

 in the area always exhibits a deep reddish-purple colour. This colour is due to 

 iron staining of the base, the origin of the iron in all probability being connected 

 with devitrification. It possesses phenocrysts of felspar, and in addition a large 

 number of flat amygdules, sometimes filled with carbonates. Examination under 

 the microscope shows the rock to be a potash-rhyolite. It does not occur very 

 far along the strike, but has been found at Martin's Creek. It is overlain by 

 a white felsite which is succeeded by a normal conglomerate. This is followed 

 by a thin flow of biotite-quartz-keratophyre, which has much in common with 

 the main keratophyre occurring near the base of the section. The flow here pos- 

 sesses a more finely-grained phase towards its upper surface, in spite of its 

 small thickness, and in this upper phase the felspar is less sodic and less abun- 

 dant. Heavy conglomerates succeed this horizon, and the repeated succession of 

 lava and conglomerate hereabouts gives rise to a series of small escarpments and 

 dip-slopes which are somewhat unique in appearance. 



The next unit is a thin flow of potash-rhyolite, the quartz being very abun- 

 dant in well-formed hexagonal crystals, the orthoclase having a less regular de- 

 velopment. Upon the rhyolite lies a distinctive conglomerate in which the sort- 

 ing of the pebbles, which in places are subangular, has not been as complete as 

 in the lower horizons. There is also a lack of continuity along some horizons, 

 and this feature, together with the presence of current bedding, points to rapid 

 accumulation of these rocks. The top portion of this horizon is really a coarse 

 sandstone or grit, and the contact effect of the overlying daeite has been to con- 

 vert this into a quartzitic rock. The daeite is an oligoclase type with a devitri- 

 fied groundmass. It weathers slowly and forms a resistant unit, in one place 

 preserving the main ridge by. its opposition to erosion. Immediately upon it 

 lies another massive rock which contains phenocrysts of quartz and felspar, the 

 identity of the latter being very difficult to determine, the results of examination 

 suggesting orthoclase. 



This is the last massive horizon coming into the section, and from here 

 through the rather rough country at the back of the Gilmore Ridge, the rest of 

 the Volcanic Stage is followed with difficulty. Tuffs with bands of small peb- 

 bles follow the last-mentioned horizon, and carry on down a long dip-slope where 

 a peculiar horizon is encountered. This appears to be a volcanic conglomerate, 

 which has resulted from the pouring out of a lava upon some unconsolidated 

 gTavel or shingle. There is a fair variety of type among the pebbles, but the 



